1. Field of the Invention
The present invention relates to a tire uniformity measuring apparatus for measuring variations in the load imposed radially of the tire through a simple arrangement.
2. Description of the Prior Art
One of the factors which govern vibrations, noise, and drivability of a vehicle is considered to be tire uniformity, that is, the appearance, dimensions and uniform rigidity of a tire. A variety of tire uniformity measuring apparatus have heretofore been proposed and put to use for checking such tire uniformity.
Known tire uniformity measuring apparatus include a rotatable cylindrical drum for rotating a tire to be measured. The drum and the tire are spaced at a fixed interaxial distance for measuring a variation (hereinafter referred to as "R.F.V.") in a reactive force acting radially of the the tire on the drum shaft or tire shaft while the drum and the tire are in rolling movement. With the interaxial distance between the drum and the tire being fixed, the entire apparatus should have an increased rigidity. The drum should be rotated at a high speed which is a few tens of revolutions per minute. The conventional apparatus is required to have a complicated electric measuring circuit. The prior apparatus is therefore disadvantageous in that it is large in size, costly to manufacture, and requires a long period of time for measurements.
In an effort to develop a tire uniformity measuring apparatus which will solve the problems the conventional apparatus has suffered, the present inventors have made systematic experiments and theoretical analyses and as a result have devised a tire uniformity measuring apparatus as described in Japanese Patent Application No. 55-166130 (U.S. patent application No. 317,727, hereinafter referred to as "prior invention"). With such a tire uniformity measuring apparatus, the interaxial distance between the tire as it rolls under a certain load and the drum is not fixed, but the rotatable shaft to which the tire is affixed is allowed to be displaced slightly for permitting a force corresponding to the axial reactive force to be detected as a displacement of a movable member. The measuring apparatus can measure a variation in a radial force acting on a tire to a nicety under a condition approximating an actual road running condition. The measuring apparatus can also be handled with ease, is light in weight, compact and less costly to construct.
However, when the tire is subjected to a large localized deformation, a large lateral force component is generated in a surface in which the tire and the drum are held in contact with each other, and a moment due to such lateral force component results in an increased variation in R.F.V. derived, which needs to be compensated for. Accordingly, the proposed prior art apparatus has suffered from an influence by such a lateral force component.